private void renamePackage(
     IPackageFragment pack, IProgressMonitor pm, IPath newPath, String newName)
     throws JavaModelException, CoreException {
   if (!pack.exists())
     return; // happens if empty parent with single subpackage is renamed, see
             // https://bugs.eclipse.org/bugs/show_bug.cgi?id=199045
   pack.rename(newName, false, pm);
   if (fCompilationUnitStamps != null) {
     IPackageFragment newPack =
         (IPackageFragment)
             JavaCore.create(ResourcesPlugin.getWorkspace().getRoot().getFolder(newPath));
     if (newPack.exists()) {
       ICompilationUnit[] units = newPack.getCompilationUnits();
       for (int i = 0; i < units.length; i++) {
         IResource resource = units[i].getResource();
         if (resource != null) {
           Long stamp = fCompilationUnitStamps.get(resource);
           if (stamp != null) {
             resource.revertModificationStamp(stamp.longValue());
           }
         }
       }
     }
   }
 }
  @Override
  Change doPerformReorg(IProgressMonitor pm) throws CoreException, OperationCanceledException {
    String name;
    String newName = getNewName();
    if (newName == null) name = getCu().getElementName();
    else name = newName;

    // get current modification stamp
    long currentStamp = IResource.NULL_STAMP;
    IResource resource = getCu().getResource();
    if (resource != null) {
      currentStamp = resource.getModificationStamp();
    }

    IPackageFragment destination = getDestinationPackage();
    fUndoable = !destination.exists() || !destination.getCompilationUnit(name).exists();

    IPackageFragment[] createdPackages = null;
    if (!destination.exists()) {
      IPackageFragmentRoot packageFragmentRoot = (IPackageFragmentRoot) destination.getParent();
      createdPackages = createDestination(packageFragmentRoot, destination, pm);
    }

    // perform the move and restore modification stamp
    getCu().move(destination, null, newName, true, pm);
    if (fStampToRestore != IResource.NULL_STAMP) {
      ICompilationUnit moved = destination.getCompilationUnit(name);
      IResource movedResource = moved.getResource();
      if (movedResource != null) {
        movedResource.revertModificationStamp(fStampToRestore);
      }
    }

    if (fDeletePackages != null) {
      for (int i = fDeletePackages.length - 1; i >= 0; i--) {
        fDeletePackages[i].delete(true, pm);
      }
    }

    if (fUndoable) {
      return new MoveCompilationUnitChange(
          destination, getCu().getElementName(), getOldPackage(), currentStamp, createdPackages);
    } else {
      return null;
    }
  }